High pressure studies on a nematogen with highly polar molecules: Evidence for a nematic–nematic transition

Abstract

We have modified a high pressure optical set-up to enable measurements on the optical path difference of aligned liquid crystals. We present the phase diagram of a polar nematogen, viz. p-cyanophenyl p-n heptyl-benzoate which is shown to exhibit a nematic (Nd) to nematic (N1) transition in the bulk at elevated pressures. We have also measured the temperature variations of the orientational order parameter (S) at various pres-sures to find that S has constant values at both the nematic to isotropic and Nd to N1 transitions at differ-ent pressures.